It is known that many oxygen sensitive products, including food products such as meat and cheese, smoked and processed luncheon meats, as well as non-food products such as electronic components, pharmaceuticals, and medical products, deteriorate in the presence of oxygen. The oxidation of lipids within the food product can result in the development of rancidity, and the oxidation of flavor components, pigments, or vitamins could adversely affect the quality and freshness of foods. These products benefit from the use of oxygen scavengers in their packaging.
Some of these oxygen scavengers, typically unsaturated polymers or polymers containing benzylic hydrogens or hydrogens adjacent to heteroatoms or tertiary carbons, in compositions with transition metal catalysts, can be triggered by actinic radiation. Triggering, as the term is used herein, offers the advantage of an oxygen scavenger that does not prematurely scavenge oxygen until such time as the user decides to use the oxygen scavenger in a commercial packaging environment. The oxygen scavenger is thus “dormant” until it is passed through an exposing unit, such as a bank of UV lights through which a package structure containing an oxygen scavenger is passed to trigger the oxygen scavenging activity of the material. This is usually done just prior to a packaging step, in which a package comprising the oxygen scavenger is made, with an oxygen sensitive product placed in the package prior to closure of the package to extend the shelf life of the oxygen sensitive product.
In many cases, packagers desire high speed packaging processes. For example, packaging lines having a speed of greater than about 40 feet per minute are known in various food packaging processes. Unfortunately, triggering of the type of oxygen scavenger just described requires actinic radiation exposure having a certain energy quantity. Since the energy quantity applied is proportional to the product of the output per unit time of the energy source and the duration of the dose, it is difficult for a packaging line on which triggering of an oxygen scavenger is desired to operate at a speed greater than about 20 feet per minute under a typical quantity of UV lamps; the faster the package assembly line speed, the less the duration of the dose, and thus the greater the energy output per unit time required from the energy source. Conventional triggering equipment is already quite large, and to achieve higher speeds with this technology would require equipment capable of applying greater energy quantities to the scavenger. The size and associated costs of purchasing or leasing such equipment, maintenance costs, safe operation costs, and the requirement of space in the processing plant to accommodate such equipment, can be economically unattractive. Some processors or potential users of oxygen scavengers do not have room for large equipment.
A class of oxygen scavengers that do not require actinic triggering, and thus do not require the associated actinic triggering equipment, includes iron based scavengers and some polymeric scavengers. Such oxygen scavengers are active at the time of manufacture without triggering by actinic radiation. These oxygen scavengers also have several disadvantages, however. Some require the presence of moisture to initiate oxygen scavenging, i.e., are moisture-triggered. This may not be technically attractive in packaging environments where it is otherwise undesirable or impractical to provide a moisture source to trigger the oxygen scavenger. Also, optics of the finished package can often be undesirably compromised by discoloration or pigmentation of the oxygen scavenger itself, either in its original state or after a period of oxygen scavenging activity. Processing of these oxygen scavengers in a uniformly dispersed way can also prove difficult in conventional extrusion operations. If such scavengers are not dispersed, as is the case with iron based sachets, scavenging activity may be too localized, and uniformity of scavenging may thus not be sufficient in the entire package environment to provide proper and adequate removal of oxygen from the head space of the package, and/or active barrier from subsequent ingress of oxygen from outside the package. Furthermore, oxygen scavenging sachets are unsuitable for vacuum packaging applications.
A solution to these problems may be to provide a multi-step process of triggering an oxygen scavenger using an initial dose of actinic radiation followed by a final dose of actinic radiation at a later time. The initial dose gives the oxygen scavenger a low dose of actinic radiation that is insufficient to trigger oxygen scavenging activity. The initial dose of actinic radiation can, however, reduce the amount of actinic radiation required for triggering in later processing steps. The cumulative dose of the initial dose and final dose is sufficient to trigger oxygen scavenging activity.
This solution avoids the need to apply a single, large dose of actinic radiation to the oxygen scavenger at a customer location, and can at least in some cases avoid the need to store a triggered, active oxygen scavenger in a container such that the oxygen scavenger exhibits no substantial oxygen scavenging activity while inside the container.